ABB Relion 670 Series Applications Manual page 252

Section 10
Multipurpose protection
Furthermore the other built-in protection elements can be used for other protection and alarming
purposes (for example, use OC2 for negative sequence overcurrent alarm and OV1 for negative
sequence overvoltage alarm).
10.1.4.3 Generator stator overload protection in accordance with ANSI or IEEE
standards
Example will be given how to use one CVGAPC function to provide generator stator overload protection
in accordance with ANSI or IEEE standard if minimum-operating current shall be set to 115% of
generator rating.
The generator stator overload protection is defined by ANSI or IEEE standard for turbo generators in
accordance with the following formula:
=
t
op
æ
I
ç
I
è
EQUATION1743-ANSI V1 EN-US
where:
t
op
TD
I
m
I
r
This formula is valid in the range of 10 s to 120 s, that is for stator current between 115% and 218% of
the generator rated current.
By defining parameter x equal to the per unit value for the desired pickup for the overload protection in
accordance with the following formula:
EQUATION1755-ANSI V2 EN-US
Equation 83
generator stator overload characteristic:
=
t
op
æ
ç
x I
è
EQUATION1744-ANSI V1 EN-US
In order to achieve such protection functionality with one CVGAPC functions the following must be done:
246
TD
2
ö
-
m 1
÷
ø
r
is the operating time of the generator stator overload protection
is the generator capability constant in accordance with the relevant standard (TD = 37.5 for either the ANSI or
IEEE standards)
is the magnitude of the measured current
is the generator rated current
can be re-written in the following way without changing the value for the operate time of the
1
×
TD
2
x
2
ö
I 1
-
m
÷
×
2
x
ø
r
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1MRK 505 370-UUS Rev. K
M13088-81 v4
(Equation 83)
(Equation 84)
(Equation 85)
Busbar protection REB670
Application manual